[unreadable] Diabetic nephropathy (DN) is the most frequent cause of renal failure in the US. Human studies show that the loss of a specific glomerular cell, the podocyte, underlies the development of proteinuria and glomerular scarring in DN, both events leading to renal failure. One process leading to podocyte loss is in-situ apoptosis. Recent animal studies revealed that podocyte apoptosis is an early feature in diabetes nephropathy. However, the mechanisms that cause podocyte apoptosis are not well understood. In this grant proposal, we propose to investigate factors and mechanisms leading to podocyte apoptosis and to determine the relationship with the development of diabetic nephropathy. [unreadable] In the first aim, we will investigate in vitro and in vivo mechanisms leading to podocyte apoptosis in diabetes. First, we will examine the in vitro mechanisms leading to high glucose mediated podocyte apoptosis using an immortalized human podocyte line and an immortalized mouse podocyte line. .Second, we will investigate the effects of physiologic and pharmacologic insulin levels on in vitro podocyte apoptosis. Then we will explore the role of Protein-kinase C (PKC) in mediating high glucose induced apoptosis both in vitro and in vivo. [unreadable] In the second specific aim, we propose to investigate factors that influence the podocyte apoptotic response. We will test the hypothesis that the cyclin-dependent kinase p27 is protective against podocyte apoptosis in vitro and in vivo. Next we will focus on the effect of matricellular proteins on glucose-induced apoptosis in vitro. Finally, we will investigate the anti-apoptotic effects of a vitamin A derivative called all-trans retinoic acid (ATRA) on podocyte high glucose mediated apoptosis in vitro. [unreadable] While podocyte number has been linked with the development of DN, we propose to further correlate this relationship through the use of a trangenic mouse in which the podocyte number can be selectively reduced. Accordingly in the third specific aim, we will induce diabetes in mice with a lower podocyte number and compare progression to their littermates as controls. Secondly, we will utilize this model as a tool to develop a mouse model more consistent with human DN. Finally, using this model, we will test the effectiveness of ATRA in slowing the progression to diabetic nephropathy. [unreadable] These proposed studies investigate the mechanisms leading to podocyte loss via apoptosis in DN with the goal to better understand this disease process, develop a new mouse model of DN, and lead to targeted therapies that slow the development and progression of DN. [unreadable] [unreadable]